JPH1120976A - Sheet feeding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeding device capable of reducing the rubber distorting amount of the outer peripheral tangential direction of a roller surface while securing a nip width by a simple structure. SOLUTION: The surface layer part 1a of one roller 1 of a roller pair 1A press-contacted for feeding a sheet is composed of a concentric-circular rubber layer using two or more kinds of rubber, the thickness of a rubber layer 3 as the surface layer of the surface layer part 1a is made thinner than that of a lower rubber layer 4, the rubber hardness of the surface rubber layer 3 is set higher than that of the lower rubber layer 4 and, thus, while securing a nip width, the rubber distorting amount of the outer peripheral tangential direction of the roller surface is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus provided in an image forming apparatus such as a copying machine or a laser beam printer and provided with a pair of rollers for conveying a sheet such as paper. Things.

[0002]

2. Description of the Related Art In a conventional image forming apparatus such as a copying machine or a laser beam printer, a sheet conveying device having a pair of rollers for conveying a conveying material (hereinafter, referred to as a sheet) such as paper is provided. As such a pair of transport rollers, at least one of the rollers is made of a high-hardness shaft such as a metal (hereinafter referred to as a core) and a low-hardness material such as a cylindrical rubber around the core. The roller is constituted by a surface layer portion formed by being mounted, and the roller and the other roller are pressed against each other to carry a sheet in a contact area (referred to as a nip area) generated between the two rollers. is there.

Here, these two rollers form a nip area by deformation of rubber caused by pressing force applied to the shaft end by a spring or the like. At this time, as shown in FIG. It is stretched in the tangential direction of the outer periphery, that is, has a tensile strain. In the figure, 6a is the core metal of the rubber roller 6,
Reference numeral 7 denotes a hard roller pressed against the rubber roller 6, and reference numeral 8 denotes a line representing the deformation of the rubber of the rubber roller 6.

[0004] Incidentally, the rubber distortion in the tangential direction of the outer periphery of the roller is a major factor in changing the transport speed. Specifically, if the force on the paper, such as the back tension, is ignored, the paper transport speed increases by the same percentage as the amount of rubber distortion in the tangential direction of the outer periphery of the roller.

On the other hand, the core metal 6a of the rubber roller 6 is bent by the pressing load. When the metal core 6a bends in this way, the axial end of the metal core 6a becomes closer to the central part due to the bending, and thereby the end nip region is compared with the central nip region. As a result, the rubber distortion in the tangential direction of the roller outer periphery is larger at the end than at the center.

[0006] In this state, if the pressing load at both ends of the core metal becomes non-uniform on the left and right due to the effect of the gear levitation force, the nip width and the rubber distortion in the tangential direction of the roller outer periphery become non-uniform in the axial direction. This causes sheet skew. In addition, the rubber distortion in the tangential direction of the roller outer periphery or the non-uniformity of the distortion in the axial direction applies a complicated force in the in-plane direction of the sheet, resulting in paper wrinkles occurring in the fixing roller or the like.

[0007]

Therefore, in the conventional sheet conveying device, the unevenness of the nip width in the axial direction can be reduced by increasing the bending rigidity of the metal core to reduce the amount of axial deflection, or to reduce the left and right nip width. The spring pressure is finely adjusted in consideration of the gear levitation force so as to be uniform, thereby reducing the left-right non-uniformity of the nip width, thereby solving the problem of conveyance such as the deviation of parallelism.

As disclosed in Japanese Patent Publication No. 6-2537, for example, a drum-shaped roller is used as a registration roller, and a roller at the center of the roller is used as a pre-transfer roller provided between the photosensitive drum and the registration roller. There has been proposed a structure in which wrinkles are prevented by using a reverse-type roller having a larger end diameter than that of the roller.

However, when such a measure is taken, problems such as a troublesome adjustment and a complicated structure arise.

The present invention has been made in view of such a situation, and provides a sheet transporting apparatus which has a simple structure and can reduce the amount of rubber distortion in the tangential direction of the roller outer periphery while securing a nip width. It is intended to provide.

[0011]

According to the present invention, there is provided a pair of rollers which are pressed against each other so as to convey a sheet, and at least one of the rollers of the pair of rollers is mounted around a shaft having high hardness such as metal and the like. And a surface layer formed of a low hardness material such as rubber, wherein the surface layer is formed of a concentric rubber layer using two or more types of rubber, and a surface layer of the surface layer is formed. The thickness of the rubber layer is smaller than the thickness of the lower rubber layer, and the rubber hardness of the surface rubber layer is higher than the rubber hardness of the lower rubber layer.

In the present invention, a rubber having a rubber hardness of 50 degrees or more and JIS-A hardness of 1 mm or less is used as the surface rubber, and a rubber having a hardness of 50 degrees or less of JIS-A hardness is used as the lower rubber. It is characterized in that it is used.

According to the present invention, there is provided a roller pair which is pressed to convey the sheet, and at least one of the roller pair is made of a shaft having a high hardness such as metal and a rubber or the like mounted around the shaft. In a sheet conveying device constituted by a surface layer portion formed of a material having a low hardness, the surface layer portion is formed of rubber, and the hardness of the rubber is higher near the surface of the surface layer portion, and the hardness of the shaft is higher. It is characterized in that the lower one is lower.

Further, as in the present invention, the surface layer of one roller of the roller pair pressed against the sheet to be conveyed is constituted by a concentric rubber layer using two or more types of rubbers, while the surface layer is the surface layer of the surface layer. By making the thickness of the rubber layer thinner than the thickness of the lower rubber layer and making the rubber hardness of the surface rubber layer higher than the rubber hardness of the lower rubber layer, the nip width is ensured and the outer circumferential tangential direction of the roller surface is maintained. Reduce the amount of rubber distortion.

[0015]

Embodiments of the present invention will be described below.

FIG. 1 is a view showing a conveying roller pair of a sheet conveying apparatus according to an embodiment of the present invention. In FIG. 1, 1A is a conveying roller pair, and 1 is a rubber roller which is one of the roller pair 1A. Reference numeral 2 denotes a hard roller made of a material having high rigidity such as metal which is pressed against the rubber roller 1,
In this embodiment, the outer diameter of both rollers 1 and 2 is φ10
mm. Reference numeral 5 denotes a metal core.

The rubber roller 1 is composed of two or more concentric rubber layers using two or more types of rubber. In the present embodiment, the surface rubber layer 3 has a small rubber thickness and a high rubber hardness. It has a surface portion 1a composed of two layers, a lower rubber layer 4 having a large thickness and a low rubber hardness. In the present embodiment, the surface rubber layer 3 has a rubber hardness of JI.
Rubber having a SA hardness of 50 degrees or more and a rubber thickness of 1 mm or less is used, and a rubber having a JIS-A hardness of 50 degrees or less is used as the lower rubber layer 4.

Since the rubber distortion in the tangential direction of the outer periphery of the roller surface is a main cause of the change in the conveying speed, the skew, and the wrinkling as described above, it is sufficient to reduce the rubber distortion. The nip width must be secured to a certain degree or more for stability. However, in the case of the conventional rubber roller 6 (see FIG. 7), if the required nip width is provided, the rubber escapes inside the nip due to the incompressible nature of the rubber by the amount that the rollers 6 and 7 are pushed together. As a result, rubber distortion in the tangential direction of the outer periphery of the roller surface increases.

On the other hand, when the surface layer portion 1a is made up of the surface rubber layer 3 having a small rubber thickness and high rubber hardness and the lower rubber layer 4 having a low rubber hardness as in the present invention, the surface rubber layer 3 is thin, There is almost no external rigidity, and the nip is formed mainly depending on the deformation of the lower rubber layer 4.

Then, the surface layer portion 1a thus configured
When a predetermined nip width is provided between the rollers 1 and 2, the lower rubber layer 4 swells to the extent that the lower rubber layer 4 is pushed in.
Since the surface rubber layer 3 is not significantly deformed by a tensile load, the outer circumferential tangential distortion of the surface of the surface layer portion 1a on the surface of the rubber roller 1 does not increase.

FIG. 2 is a diagram schematically showing this state. In FIG. 2, numeral 14 denotes a line representing the shape of the rubber which was a straight line before deformation and the shape of the rubber after deformation. The actual deformation state is exaggerated.

As is apparent from this figure, the surface layer 1a is made of a surface rubber layer 3 having a small rubber thickness and a high rubber hardness.
And the lower rubber layer 4 having a large rubber thickness and a low rubber hardness can significantly reduce tangential rubber distortion on the roller surface as compared with the conventional rubber roller 6 even when having the same nip. Therefore, a change in the transport speed can be suppressed to a small value.

Further, even when the nip width of the cored bar 5 is non-uniform in the axial direction, the amount of distortion in the axial direction is not so nonuniform because the original amount of rubber distortion on the roller surface is small. Paper wrinkles can be minimized.

Next, a first example of this embodiment will be described.

In this example, the thickness of the surface rubber layer 3 was 50 μm, the hardness of the rubber was 85 degrees, the rubber thickness of the lower rubber layer 4 was 1.5 mm, and the hardness was 25 degrees.

FIG. 3 is a graph comparing the distribution of contact pressure in a section perpendicular to the core metal between the conventional roller 6 and the rubber roller 1 of the present embodiment. However, the conventional roller 6 is a single layer of rubber having a rubber thickness of 1.5 m and a rubber hardness of 45 degrees. This graph shows the contact pressure of only the right half of the cross section. The horizontal axis of the graph is the roller surface position, and the vertical axis is the contact pressure.

In the figure, reference numeral 15 denotes a contact pressure distribution of the present embodiment, and reference numeral 16 denotes a contact pressure distribution when a conventional roller is used. However, the pressing force required to obtain the contact pressure shown in this graph is about half in the case of the present embodiment as compared with the case of the conventional example.

FIG. 4 is a graph comparing the distortion of the rubber surface at the time of pressing between the conventional type and this embodiment. In the drawing, reference numeral 17 denotes a rubber surface strain distribution of the present embodiment, and reference numeral 18 denotes a rubber surface strain distribution when a conventional roller is used.

As can be seen from the graphs of FIGS. 3 and 4, the distortion at the time of pressing to obtain the same nip width is as follows.
In the nip, the rubber roller 1 of the present embodiment is overwhelmingly smaller than the conventional roller 6.

Therefore, when the rubber roller 1 according to the present embodiment is used, a certain amount of nip width can be formed with a very small amount of rubber surface distortion, and problems such as speed change, skew, and paper wrinkling during sheet conveyance are minimized. It becomes possible to suppress to.

This is the case where the surface layer 1a is formed by two rubber layers 3 and 4. However, even when the surface layer 1a is formed by three or more rubber layers, the surface Between the lower rubber layers, the relationship described above, that is, the thickness of the surface rubber layer is made smaller than the thickness of the lower rubber layer, and the rubber hardness of the surface rubber layer is made smaller than the rubber hardness of the lower rubber layer. A similar effect can be obtained by keeping it high.

Next, a second example of this embodiment will be described.

In this embodiment, the hardness of the surface rubber layer 3 of the rubber roller 1 is changed from 85 degrees in the first embodiment to 75 degrees and 65 degrees. FIG. 5 shows the contact pressure distribution when the hardness of the surface rubber layer 3 is changed as described above.

In the figure, 19 is the contact pressure when the surface rubber hardness is 85 degrees, 20 is the contact pressure when the surface rubber hardness is 75 degrees, 21 is the contact pressure when the surface rubber hardness is 65 degrees, Reference numeral 22 denotes a contact pressure when the conventional roller described in the first embodiment is used. However, the pressing force is the same as the pressing pressure of the conventional example in any case.

As can be seen from the results, the surface rubber layer 3
By adjusting the rubber hardness, the shape of the pressure distribution in the nip can be adjusted. In addition, the same adjustment can be made depending on the thickness of the rubber of the surface rubber layer 3.

By the way, in a fixing roller which is an example of a conveying roller, toner is fixed on a sheet by heat and pressure. However, if the pressure in the nip is low, fixing failure occurs, so that the pressure distribution in the nip can be efficiently reduced. You need to control.

On the other hand, the pressure distribution in the nip of the conventional roller is elliptical, but in the case of the roller according to the present embodiment, it can have a distribution close to a square. Therefore, this roller 1
In the case of, if the peak pressure is set higher than the pressure required for fixing, sufficient pressure can be applied to the sheet and toner in a wider section in the nip, and a more efficient fixing roller should be designed. Is possible. That is, if the fixing roller having the configuration according to the present invention is used, the pressure distribution in the nip can be freely adjusted by the thickness and the rubber hardness of the surface rubber.

Next, a third example of this embodiment will be described.

FIG. 6 is a view showing the configuration of a pair of conveying rollers of the sheet conveying apparatus according to the present embodiment.
Is a surface layer portion made of rubber, and this surface layer portion 1b
The hardness of the rubber is different between the portion close to the cored bar 5 and the portion close to the surface. In the figure, the difference in hardness is schematically represented by the density of the dot on the surface portion 1b. That is, rubber hardness is high in a portion near the surface of the surface layer portion 1b, and low in a portion near the cored bar 5.

The same effect as that described in the first embodiment can be obtained by using the rubber roller 1 having the configuration shown in the present embodiment.

[0041]

As described above, according to the present invention, the thickness of the surface rubber layer is made smaller than the thickness of the lower rubber layer, and the rubber hardness of the surface rubber layer is kept higher than the rubber hardness of the lower rubber layer. A simple structure that reduces the amount of distortion in the circumferential direction of the rubber surface during nip formation, and the balance between the pressing force applied to the roller end and the deflection of the roller shaft or the pressing force applied to the roller end , The change in rubber surface distortion in the roller axis direction can be reduced. As a result, when the sheet is conveyed, a change in the conveying speed, a skew, and a paper wrinkle can be minimized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a pair of conveying rollers of a sheet conveying apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a deformed state of rubber in the vicinity of a nip region in the transport roller pair.

FIG. 3 is a table showing a contact pressure distribution between a roller of a first example of the present embodiment and a roller of a conventional example.

FIG. 4 is a table showing the distribution of the amount of distortion in the circumferential direction of the rubber surface of the roller of the first example of the present embodiment and the roller of the conventional example.

FIG. 5 is a view showing the influence on the contact pressure when the hardness of the surface rubber is set to various values by the roller of the second example of the embodiment.

FIG. 6 is a diagram illustrating a configuration of a transport roller pair according to a third example of the present embodiment.

FIG. 7 is a diagram illustrating a pair of conveying rollers of a conventional sheet conveying apparatus.

[Explanation of symbols]

 1A Conveyance roller pair 1,6 Rubber roller 1a Surface layer 2,7 Hard roller 3 Surface rubber layer 4 Lower rubber layer 5,6a Core

Claims (3)

[Claims] An image forming apparatus comprising: a pair of rollers pressed against each other so as to convey a sheet; and at least one of the pair of rollers is formed of a shaft having a high hardness such as metal and a low hardness such as rubber mounted around the shaft. In a sheet conveying device constituted by a surface layer portion formed of a material, the surface layer portion is constituted by a concentric rubber layer using two or more types of rubbers, and the thickness of the rubber layer serving as the surface layer of the surface layer portion is set to a lower layer. A sheet conveying device, wherein the thickness of the rubber layer is smaller than that of the rubber layer, and the rubber hardness of the surface rubber layer is higher than the rubber hardness of the lower rubber layer. 2. The surface rubber has a rubber hardness of JIS.
-Use a rubber having a hardness of 50 degrees or more and a rubber thickness of 1 mm or less,
The sheet conveying device according to claim 1, wherein a rubber having a hardness of JIS-A hardness of 50 degrees or less is used as the lower rubber. 3. A roller pair which is pressed against the sheet so as to convey the sheet, and at least one of the rollers of the roller pair is made of a shaft having high hardness such as metal and a low hardness such as rubber mounted around the shaft. In a sheet conveying device constituted by a surface layer formed of a material, the surface layer is formed of rubber, and the hardness of the rubber is higher near the surface of the surface layer and higher on the axis. A sheet conveying device characterized by being lowered.